The HSBC's logo is seen at a bank branch in Hong Kong January 9, 2013. REUTERS/Tyrone Siu

The request comes amid concerns about the deal’s funding triggered by the possible withdrawal of a crucial loan from China Development Bank (CDB).

Reuters reported on Tuesday that CDB is reconsidering its offer to finance a substantial portion of the deal, after the Chinese and Hong Kong media said funding from CP’s first installment came from people not affiliated with CP. The company has denied the reports.

“The CIRC has received an application from Ping An Group regarding the stake transfer, conducted a preliminary review according to rules, and notified the company to provide additional materials,” the CIRC said in an emailed statement to Reuters on Thursday, without specifying what additional information it was seeking.

HSBC said the deal remains on track and it was not aware of any new information related to it that needed to be disclosed.

Europe’s biggest bank said it issued its brief statement at the request of Hong Kong’s stock exchange.

CP Group agreed to buy HSBC’s 15.6 percent stake in Ping An on December 5, backed by CDB. HSBC said, based on inquiries it had made following the media reports, the information released then “remains accurate”.

HSBC said in the original deal that the payment obligations in respect of the second tranche “are supported principally by a guarantee from CDB” and a cash deposit by CP Group.

The CIRC has set a deadline of February 1 for final approval of the transaction, which would see HSBC exit a lucrative investment that it now regards as non-core. It will make a post-tax gain of $2.6 billion.

The deal requires approval because HSBC owned more than the 5 percent threshold above which prospective owners need CIRC permission. CP Group planned to buy the stake from HSBC in two stages: an initial outright purchase of 20 percent of the shares on offer, and then a CDB-funded second offer for the remaining 80 percent.

It is this second stage that is now in jeopardy as CDB wavers in its commitment and CIRC investigates the structure of the whole transaction. Late last month, media reports in China and Hong Kong said the first CP payment came from funding sources not directly tied to the Thai conglomerate, contrary to the terms of the agreement.

“The transaction is undergoing the normal approval procedures and there is nothing further to disclose at this time,” Ping An Insurance said in an e-mailed statement on Thursday.

The failure of the deal would be a blow to HSBC and an embarrassment to the various parties involved in a deal, which would be the largest ever inbound acquisition deal in China.

CP spokeswoman Suthana Hongthong said the deal was still on. “Everything is still in process,” she said without giving details.